With Palestinian leader Yasser Arafat under increasing pressure from the United States to step aside, focus has once again shifted to potential successors.

Although no clear-cut heir to the Palestinian leader has ever emerged - largely down to Mr Arafat's own engineering - a number of names have often been cited.

These people are unlikely to mount a challenge to their own leader, but they would most likely be waiting in the wings if he were to step aside.

Possible contenders fall into two main categories - the older men who lived decades in exile with the Palestinian leader and younger ones who grew up fighting the Israelis in the West Bank and Gaza and studying Israeli society at close hand.

The 67-year-old is otherwise known as Abu Mazen. He is Yasser Arafat's deputy as head of the PLO.

Mahmoud Abbas: Obvious choice in a presidential election for the Fatah rank and file

He worked with the movement during its long years in exile in Jordan, Lebanon and Tunisia.

Analysts say his power has ebbed and flowed over the years. He is seen as a moderate and widely regarded as the architect of the Oslo peace process.

He has frequently negotiated with the Israelis and had dealings with the US, where he is regarded reasonably well.

Analysts say he would be the most obvious choice in a presidential election for the Fatah rank and file, who would have a strong interest in uniting around a single candidate.

Abu Mazen would represent continuity and would be acceptable to the vast majority of Palestinians.

However, some people see him as being too associated with the older generation to be elected as president. Another possible downside is that he has too close an involvement with the failed peace process.

The 42-year-old Secretary-General of Mr Arafat's Fatah movement in the West Bank is one of the Palestinians' most prominent political leaders.

He has been a major figure in the current intifada, or uprising and has consistently backed resistance by Fatah activists against Israeli occupation.

Marwan Barghouti: Currently in Israeli custody

He is currently in Israeli custody after being arrested during Israel's military campaign in the West Bank in April. Israel accuses him of being behind attacks on Israelis - a charge he denies.

Mr Barghouti is a charismatic and determined leader, with a large grassroots following in the West Bank. Much of his support derives from the fact that he spent a lot of time in Israeli jails during the previous Palestinian intifada.

He is a member of the Palestinian Legislative Council and would almost certainly run for his seat from jail. It is unclear whether he would run against Mr Arafat for the presidency.

Abdel Sattar Qassem, 53, is a Palestinian dissident and politics professor at al-Najah university - a bastion of the Islamic militant group, Hamas.

Abdel Sattar Qassem: Described as a rebel figure with little local support

He has been jailed by Israel and - more recently - by Palestinian security forces after criticising Mr Arafat and the Palestinian Authority, which he describes as the "most corrupt of the Arab states".

He is reported to sympathise with Islamic militant groups and supports suicide attacks against Israeli civilians.

Mr Qassem does not recognise the state of Israel and opposes the interim peace agreements Mr Arafat struck with Israel.

He is said to have no local support and has been described as a loner, a rebel figure who is not part of any political organisation.